1. Field of the Invention
The present invention relates to a suspension.
2. Discussion of Background
There are various suspensions each for hanging an axle from a chassis frame of a vehicle. Among them, leaf suspensions with layered leaf springs have been widely used for vehicles such as trucks since they are simple in structure, less expensive, of high strength and highly durable.
It is, however, undeniable that the conventional leaf suspensions are inferior in vehicle-riding comfort to the existing air suspensions. Air leaf suspensions with combined leaf and air springs have, therefore, been under development which are less expensive and have improved riding comfort.
More specifically, air leaf suspensions each comprising a leaf spring and an air spring in combination and arranged at opposite sides of a vehicle are advantageous in that only two air springs suffice for support of the axle and in that stabilizers may be omitted because of the leaf springs serving as stabilizers, leading to simplification of the whole structure. As a result, the air leaf suspensions are less expensive and have less increase in vehicle weight than conventional four-bag air suspensions each for supporting an axle by means of four air springs arranged forwards, rearwards, left and right of the axle. Such kind of air leaf suspensions have been disclosed, for example, in the applicants' JP 2003-34113A.
Basic design concept not only in the above-mentioned air leaf suspensions but also in existing conventional suspensions resides in that periaxial rolling moments (braking and driving forces) and lateral displacement moments applied on the axle are positively suppressed to allow only vertical displacement of the axle. Improvement in vehicle-riding comfort on the basis of such design concept has, however, been limitative of itself.
Because, in order to improve vehicle-riding comfort of air leaf suspensions on the basis of such existing design concept, a leaf spring made of high-strength steel with toughness and with extremely reduced thickness is to be provided for each of the sides of a vehicle so as to attain low spring constant while air springs are to be larger-sized to give added weight in effectiveness of the air springs; however, such lowered spring constant may lead to extremely lowered spring effect so that the chassis may tend to be readily rolled, resulting in a lowering of drivability.
The present invention was made in view of the above and has its object to provide a suspension which is inexpensive and light in weight and which can attain substantial improvement in vehicle-riding comfort without lowering drivability.